Fwd = Laser Search for Extraterrestrials
- Forwarded by: fwestra@... (Frits Westra)
Original Date: Thu, 28 Feb 2002 18:08:49 -0500 (EST)
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>>>> FarShores UFONewsPosted Feb 27.02
Laser Search for Extraterrestrials
A new approach to communicating with alien civilisations.
After almost 40 years of fruitless endeavour, no great or small radio
signals from extraterrestrial intelligence (ETI) have been found. The
Universe appears silent even though instruments literally billions of
times more powerful than Frank Drake's primitive one-channel radio
telescope have come online.
Drake was the first scientist to carry out a search for ETI with a
radio telescope in 1960. His predictions that we would find ETI by
the 1980s have not been realised and he has had on more than one
occasion to revise his estimates for a successful detection. The
reality is that the ETI search is a cosmic enterprise and we may not
know that ETI exist for several more decades.
This has not stopped a new group of 'young Turks' in the US and
Australia from expanding the search to the optical region of the
electromagnetic spectrum. The US effort includes Prof Paul Horowitz
from Harvard University, Dr Dan Werthimer from the University of
California and Dr Stuart Kingsley from the Columbus Optical SETI
Observatory, while the Australian effort is led by Dr Ragbir Bhathal
from the University of Western Sydney.
Bhathal's experiment is the only one in the Southern Hemisphere and
also one of the most sensitive in the world. According to Bhathal, an
award-winning author and astrophysicist: 'If ETI are out there they
would have surpassed the radio threshold and gone on to communicate
with other intergalactic civilisations by laser pulses. Light waves
carry hundreds and thousands of times more information than radio
The Universe may well be radio-silent. If this is true, radio search
strategies are in for a big surprise and all the well-laid plans for
the construction of a large telescope array may come to nought.
SETI first caught Bhathal's interest when he read Drake's 1960
article on Project Ozma in the American journal Physics Today. Being
too busy 'earning my PhD and doing real physics,' he did not give
SETI much thought. He was more interested in working on Nobel Prize
winner Louis Neel's theories on magnetism. His PhD days at the
University of Queensland were 'exciting times'. His PhD supervisor
was Prof Frank Stacey, a Fellow of the Australian Academy of Science
and the first recipient of the Neel Medal. He set the physics
community agog with his ideas on the existence of a fifth force, but
several years of searching failed to find it.
Bhathal's interest in SETI was revived in 1996 when, out of
curiosity, he attended a bioastronomy conference in Capri and heard
the inventor of the laser and Nobel Prize winner, Charles Townes,
talk about optical SETI and the possibility of ETI using lasers for
intergalactic communication. Most of the participants were sceptical
about what Townes was telling them and did not take him very
seriously, but Bhathal was sufficiently impressed with Townes' talk.
On returning home to Sydney he began his own investigations.
He was surprised to find that not much work had been done in optical
SETI. He organised an international conference on SETI and Society at
the University of Western Sydney in 1998 and launched his own optical
The idea of optical SETI is not new. In the 19th century the European
mathematician Karl Gauss proposed the use of mirrors to send light
messages to aliens on the Moon. He remarked that if we could get in
contact with the aliens on the Moon 'it would be a discovery greater
than that of America'.
Graham Bell, the inventor of the telephone, had in fact used a light
beam to transmit messages. Called the photophone, he said that it was
his greatest invention. However, since he used ordinary light it
suffered from dispersion and scattering in the atmosphere and never
saw the light of day.
The invention of the laser by Charles Townes in the 1960s provided an
extremely narrow and sharp beam. This property of the laser threw
open the possibility of using lasers to communicate. This led
Schwartz and Townes to suggest in a long-forgotten article in Nature
that lasers could be used for interstellar communication rather than
radio waves. The idea did not get off the ground because in the 1960s
lasers were considered novelties and their power was small.
In contrast radio technology, which had a head start of several
decades, was relatively mature. Thus, the scientific community
concentrated the search for ETI in the radio region of the
electromagnetic spectrum, especially at the special emission
frequency (1.4 gigahertz) of neutral atomic hydrogen - called the
'21cm line' after its wavelength.
In February 2001, Bhathal published an article in the British journal
Astronomy & Geophysics in which he made a case for carrying out
optical SETI. He said that 'Moore's Law doubling of laser
technology over the last 40 years has seen laser power rise
exponentially from the milliWatt lasers used in undergraduate
laboratories to megaWatt lasers in industry'. For instance, the
National Ignition Facility in the US has produced laser powers in the
terraWatt range (1012 Watts), albeit for short periods. These
developments, Bhathal argued, give tremendous credence to the search
for ETI signals in the form of nanosecond laser pulses.
We already have the technology that can produce extremely short laser
pulses of petaWatts (1015 Watts). If one couples this to a large
optical telescope like the 10-metre Keck, which is used like a
searchlight mirror, we have an efficient system of directing
nanosecond laser pulses at other interstellar civilisations.
Laser light produced like this and directed towards the solar system
would easily outshine the light from the star from which the light
originated. According to Bhathal, the nanosecond laser pulse would
appear about 5000-7000 times brighter than the background light from
the ETI star. This fact is independent of distance, since both the
laser light and the light from the ETI star will diminish at about
the same rate with distance.
The other advantage, according to Bhathal, is that no magic
frequencies are involved in an optical search, unlike the radio
search at the 21 cm line. 'We don't have to guess the ETI laser
wavelength,' he said. The stark difference between signal and
starlight will show up in any search that uses a broadband 'white
light' detector, such as a photomultiplier tube.
There are a number of other reasons for searching for ETI signals in
the optical region. It is well-known from observations that the
ionised hydrogen in interstellar medium causes smearing and
degradation of transmitted radio signals. While dispersion broadens
radio pulses, it is negligible at optical frequencies. The
transmitted beams from optical telescopes are sharper and narrower
than their radio counterparts.
The discovery of several other lines of astronomical interest led
Townes to question the superiority of the 21 cm line as the only
wavelength at which ETI will be transmitting signals. Kingsley
further questioned the almost religious use of the 21 cm line as the
favoured search frequency.
Together with Bhathal, Kingsley organised an international conference
on optical SETI in January 2001. It was held in Silicon Valley,
America's centre of new and exciting ideas and endeavours. Attended
by more than 100 SETI researchers and keynoted by Townes, it marked
the rise of optical SETI as a major new force in the search for ETI.
One of the great advantages of doing optical SETI, according to
Bhathal, is that 'it does not require complicated equipment and
computational power as compared with the radio search'. All that is
required is a pair of extremely fast photon-counting detectors wired
up in coincidence mode. This is similar to the coincidence techniques
used in nuclear physics, where two detectors send an alert when they
receive a signal at exactly the same moment. Very fast
photon-counters have come on the market only recently, enabling
optical SETI to take off.
Bhathal's search strategy is to look for nanosecond laser pulses
within a volume of 100 light years. These are likely to be deliberate
signals from ETI to us, rather than 'noise' generated by an advanced
civilisation communicating with itself.
There are about 1000 stars within Bhathal's search range. Assuming
that an ETI civilisation targets one star after another and fires a
laser pulse at perhaps 10 stars per second, then this civilisation
could hit all Sun-like stars every 100 seconds. Bhathal thus spends a
few minutes on each star and revisits the stars on his nightly run.
He has designed very fast and extremely sensitive detector systems
that he attaches to two telescopes separated by a few metres at his
OZ OSETI observatory at the University of Western Sydney in
Campbelltown, a semi-rural suburb about 60 km from the heart of
Sydney. Bhathal says that 'most Campbelltownians switch off their
lights and are asleep by 10 pm, thus leaving the night sky quite
dark'. Even so, light pollution does not cause a problem with optical
SETI. In fact, Kingsley says that optical SETI can be carried out
during the day with suitable filters.
In Bhathal's set-up, light from the telescopes is split by
beam-splitters and falls on very fast photomultiplier tubes wired in
coincidence mode to reject any false signals. He uses two telescopes
to ensure that the system is not bugged by false hits during an
observation run. His system is different from that of his American
counterparts and is much more sensitive to ETI signals. By keeping
track of the light flash intensity when the paired detectors respond
simultaneously, it is possible to know whether ETI has sent a signal.
Distant lightning flashes or static electricity or other extraneous
fast flashes of light do not pose a problem for Bhathal's detector
system since these flashes are not in the nanosecond range.
After almost a year's observations of 100 Sun-like stars and 15
globular clusters, no evidence of intentional laser signals have been
found. So what are his plans for the future? Bhathal says he will
continue to monitor another 2000 stars, 30 globular clusters and a
few galaxies. He has also drawn up plans for the construction of a
1-metre dedicated optical SETI telescope to carry out an all-sky
survey. The wide-field telescope will carry out a meridian transit
survey in which the night sky will drift through the field of view of
his stationary telescope. 'The telescope will be used as a light
bucket and it will not need to be highly accurate,' he said. 'A few
arcminutes would be sufficient for the purposes of the project.' The
whole southern sky would be covered in about 250 clear nights.
In case he does discover a signal he has a bottle of champagne in his
observatory to celebrate the event.
Story originally published by:
Australasian Science [March] | David Davids - Feb 26.02
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